Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities
Net income	$ 64,769	$ 80,457
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,174	11,779
Amortization of operating lease right-of-use assets	1,596	1,664
Stock-based compensation expense	8,099	7,424
Deferred taxes	(643)	591
Other	(1,229)	(74)
Changes in operating assets and liabilities:
Decrease (Increase) in accounts receivable	(11,699)	(7,880)
(Increase) in receivables from broker-dealers, clearing organizations and customers	(296,015)	(270,491)
(Increase) decrease in prepaid expenses and other assets	(2,445)	3,082
(Decrease) Increase in accrued employee compensation	(33,553)	(34,103)
Increase in payables to broker-dealers, clearing organizations and customers	229,151	174,942
(Decrease) increase in income and other tax liabilities	3,049	4,814
(Decrease) increase in accounts payable, accrued expenses and other liabilities	1,932	2,599
(Decrease) in operating lease liabilities	(1,799)	(1,845)
Net cash provided by operating activities	(23,730)	(23,159)
Cash flows from investing activities
Purchases of furniture, equipment and leasehold improvements	(1,396)	(4,257)
Capitalization of software development costs	(9,425)	(8,075)
Net cash (used in) provided by investing activities	(10,821)	(12,332)
Cash flows from financing activities
Cash dividend on common stock	(27,425)	(25,454)
Exercise of stock options	50	244
Withholding tax payments on restricted stock vesting and stock option exercises	(20,292)	(27,422)
Repurchases of common stock	(38,800)	(520)
Proceeds from short-term borrowings	100,000	69,302
Repayments of short-term borrowings	(100,000)	(35,000)
Net cash (used in) financing activities	(86,467)	(18,850)
Effect of exchange rate changes on cash and cash equivalents	(4,356)	(1,027)
Cash and cash equivalents including restricted cash
Net (decrease) increase for the period	(125,374)	(55,368)
Beginning of period	625,567	608,050
End of period	500,193	552,682
Supplemental cash flow information
Cash paid for income taxes	8,487	6,250
Cash paid for interest	134	191
Non-cash activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	91	878
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	0	(5,495)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	$ (117)	$ (1,613)